1. Field Of The Invention
The present invention relates to a wedge-type expansion assembly particularly adapted for expanding brake shoes of brake assemblies in motor vehicles.
2. Description Of The Prior Art
Wedge-type expansion devices of the general type to which the present invention relates are previously known as, for example, shown in German Pat. No. 2,356,075. This patent shows a device wherein the two ends of the rollers of the roller cage are provided with a guide trunnion projecting over the front face of the roller. The guide trunnions engage in an axially continuous opening in a flank of the roller cage. This prior known device has several disadvantages and drawbacks in that the guide trunnions of the rollers have a relatively small radial guide face and therefore, when subjected to heavy stress in operation, are subject to damage by sliding wear. A further disadvantage results by reason of the fact that rollers provided with guide trunnions are difficult to produce since the guide trunnions must be shaped precisely concentrically with the active rolling face of the roller. It has been found that when the rollers are hardened, harmful internal stresses and hardening cracks are often produced at the transition of the front face of the roller and the guide trunnion. Additionally, the radial bearing capacity of the rollers is also limited since the active length of the rolling face of the rollers is reduced in size by the axial extension of the two-guide trunnions. Further, these prior known expansion wedge devices for expanding brakes of motor vehicles, the construction space for accommodating large bearings capable of withstanding the loads, cannot always be provided.